Conventionally, various types of operation-detecting sensors that detect an operation performed on an operation surface by an operator have been devised. Examples of operation-detecting sensors include a capacitive type, a thermal resistance type, piezoelectric acoustic type, an infrared sensor type, and the like. In order to detect a pressing force applied to an operation surface, it is necessary to install a pressure-detecting sensor that is different from these types of operation-detecting sensors.
Patent Literature 1 discloses a touch input device including a touch panel that serves as an operation-detecting sensor and a pressure-sensitive sensor that detects a depression of an operation surface. In the touch input device of Patent Literature 1, the pressure-sensitive sensor is placed on a lower surface of the touch panel (i.e., a surface opposite to the operation surface), and is equal in area to the touch panel.
Further, in the touch input device of Patent Literature 1, the operation surface of the touch panel is covered with a protective layer.
Patent Literature 2 discloses an operation input device having matrices of electrodes formed on both sides of a flat-plate piezoelectric body.
Patent Literature 1: JP 5-61592 A
Patent Literature 2: JP 2006-163618 A